Facebook announced early Monday that it had acquired Onavo, a three-year-old start-up that makes data compression software and offers a variety of analytic services for smartphone applications.

The purchase of Onavo, which has about 40 employees, gives Facebook, the world’s biggest social networking company, its first office in Israel.

Most of Facebook’s employees work at its headquarters in Menlo Park, California, and historically, the company has sought to pull workers at acquired companies into the mother ship. But Onavo cut a deal to keep most of its employees in Tel Aviv as part of the sale, which was for about $120 million, according to a person familiar with the terms.

The big draw for Facebook is Onavo’s pioneering data compression technology, which helps smartphones cut data consumption as much as 80 percent. Such compression is vital to the goals of Internet.org, an organization started by Facebook’s chief executive, Mark Zuckerberg, in August that is trying to offer mobile Internet access free or at very low cost to the about four billion people globally who do not have it.

‘‘We expect Onavo’s data compression technology to play a central role in our mission to connect more people to the Internet, and their analytic tools will help us provide better, more efficient mobile products,’’ a Facebook spokesman said.

Guy Rosen, co-founder and chief executive of Onavo, said that his company would largely function as a stand-alone entity, much like two previous Facebook acquisitions, Instagram and Parse. (Snaptu, another Israeli start-up with innovative data compression technology, was absorbed into Facebook after it was purchased in 2011, and its technology forms the basis of the company’s Facebook for Every Phone software for more basic phones.)

‘‘We’re excited to join their team and hope to play a critical role in reaching one of Internet.org’s most significant goals — using data more efficiently, so that more people around the world can connect and share,’’ Mr. Rosen wrote in a blog post announcing the sale. ‘‘When the transaction closes, we plan to continue running the Onavo mobile utility apps as a stand-alone brand.’’

A version of this article appears in print on 10/15/2013, on page B3 of the NewYork edition with the headline: Facebook Buys Israeli Maker of Data-Compression Software for Mobile Web Effort.